Scanning antenna system



1951 w. c. WILKINSON, JR 5 5 SCANNING ANTENNA SYSTEM Filed Jan. 21, 1950 ATTORNEY This invention relates to .energy scanning apparatus and focusing devices.

Patented Nov. 27, 1951 2,576,182 .SCANNINGANTENNA SYSTEM, 1

William C. Wilkinson, Jr., Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 21, 1950, serial No. 139,859

electromagnetic It is frequently desirable in scanning an area from an antenna to radiate or receive a collimated beam of energy in a complete 360 circular scan around the antenna.

Such scans of 360 are often desired; for example, in radio echo detection devices. This type of scanning is most often accomplished by rotating an entire antenna including afocusing reflector which is rotated through the desired 360 scan angle. However,

of. scanning is often slow, and the requisite equipment, is often bulky. It has been proposed. in the application of Harley Iams, Serial No. 782,521, filed October 28, 1947, to provide a lens especially adapted for scanning purposes whereby an associated feed devicem'ay be rotated around the circular periphery of the lens. This lens of the Iams application, however, operates only for energy polarized'with the electric vector normal to the plane of the circular edge of the lens and to the scan circle, It is an object of the present invention to pro vide anantenna apparatus for scanning through a complete circle with energy polarized-parallel to the plane of the scan circle. It is a further object of the invention to provide a lens element suitable for such apparatus.

It is a further object of the invention to-provide such apparatus which is readily constructed, compact, and permits of rapid scanning by rotation of a horn feed or the like.

These and other objects, advantages; and

novel features of the invention will be more apparent from the following description in which like reference numerals refer to like parts and 4 in which:

Fig. 1 is a plan view from above of apparatus according to the invention; and

Fig. 2 is a view partiallyin cross section along sectionline 2 -2; of Fig.- 1.

,In accordance with :the invention 'a pair of dielectrically separated metallic bodies have wave-guiding surfaces facing each other between which: the energy is to pass. The wave-guiding surfaces are each rotationally symmetrical with respect to a common axis, and the spacing therebetween is predetermined so that collimated energy entering the circular edge of the space between the bodies is focused at another point on the edge of the space. The metallic bodies preferably comprise a metallic coating on a dielectric member. A radiator or receptor placed at the focal point may then be rotated along the circu-,

-8 Claims. (Cl. 250-33153) lar edge of the space between the wave-guiding surfaces. 1 Referring now more particularly to the drawing, a lens element or focusing device 8 includes a pair of metallic bodies l0, l2 having wave-guiding surfaces l4 and I6 respectively facing each other defining therebetween a space I8 filled with a dielectric medium. In the example shown, the space l8 isfilled with a solid dielectric. Thesurfaces l4, l6 may comprise. metal plates juxtaposed with the upper and lower surfaces of the dielectric medium 18 or surface electrodes may be plated or otherwise applied to said medium. The space 18 has a substantially circular edge 20 which lies between the circular margins 22, 24 of the wave-guiding surfaces M, l6 respectively.

The focusing device 8 has associated :with it a radiator or receptor, such as a horn antenna, depending on whether it is desired to radiate or receive electromagnetic energy. The horn antenna 26 is closely adjacent to the edge 20, say a fraction of the edge radius, andpreferably a small fraction, say one-tenth. Horn antenna 26 at its other end is coupled to one terminalof a rectangular waveguide 28, the other terminal of which is coupled to arotary joint 30.;v The rotary joint 30 in turn is coupled to a rectangular waveguide 32, the latter being connected to a transmitter or receiver (not shown) if desired through a suitabletransmit-receive arrangement such as is customary in radio echo detection apparatus. The rotary joint 30 may be of the type disclosed at page 427 of Microwave Transmission Circuits, edited by G. L. Ragen and published as Volume 9 of the Radiation LaboratorySeries by the Massachusetts Institute of Technology. By means of two transitions 30a and 301) the rac tangular guide 32 is coupled through the rotary joint 30 to the rectangular guide 28. The horn antenna 26 feeds, or receives, through the focusing device 8, energy polarized with the electric vector in the planeof the periphery 'cir-, cular edge 20 and parallel tothe planes of the peripheries or circular'margins 22, 24. Because of the type of rotary "transition here shown, in order to obtain the desired polarization, the waveguide 28 contains a 90 twist 28a at a suitable point therein. Therotary joint 30 may be driven through suitable gearing 34 by a'motor 36. Other means for obtaining the desired circular motion of horn antenna 26 will be evident from the'various rotary joints described at pages 446 to 455 of the same volume. 1

It is known, as pointedout for examplein the volume entitledMathematical Theory of Optics the point in question;

n= if M collimated rays falling on the surface of the sphere will be focused at a point diametrically opposite, that is, the point intersected by the radius vector from the center of the sphere having the same direction as the incident raysr By analogy to plane geometric optics, if electromagnetic energy be propagated with the electric pulses of energy may be sent out from a transmitter through waveguide 32, the rotary joint 30, waveguide 28 and horn antenna 26. Thus the energy is fed to the focusing device 8 substantially at a point on the circular edge 20 of the disk-like space between the surfaces [4, l6 polarized with the electric vector parallel to the plane 46. The

' rays 'of energy; then follow paths somewhat as illustrated by the dotted raylines inside the space vector parallel to the plane of a disk-like space defined by the surfaces of two metallic bodies, then an equivalent effective index of refraction where e is the dielectric constant of the material in the space defined between the metallic bodies,

an is the-free space wavelength; and a is the spacing between the wave-guiding surfaces at Equating the values of m and 11. gives the law of .dependency or the function which the spacing-between the surfaces l 4 and I6 should obey in order to cause the energy to be focused at the circular edge 26 of the disklike space. The spacing betweenthe wave-guiding surfaces to accomplish the desired focusing is found to be;

0 a e +(R) 2 Collimated rays 38 shown schematically in Fig. 1 are thus focused at a point 40' which is intersected by the radius vector 42 drawn parallel to the rays 38 from the axis of symmetry 44 of the device 8 to the edge 20. The device 8 and the associated scanning apparatus are particularly adapted for the radiation or reception of exceedingly short wavelengths of electromagnetic energy. It is preferred to construct the device 3 by forming a polystyrene disk to fill the space defined by the metallic elements [0, 12 which may then be deposited as a metallic coating, which may be silver or the like. A typical device 8; made of polystyrene dielectric coated'with silver, and with a radius R from the axis 44 to the edge Zll of 10 inches, has substantially a half power beam width of 2 degrees and lobes reduced by 13.6 decibels from the maximum of the main lobe. The free space wavelength at the operating frequency is 1.5 centimeters and the maximum separation a. at the axis is .33 centimeters. The surfaces l4, l6 and the bodies l0, 12 are preferably symmetrical with respect to a central plane 46 between them. Then the bodies Ill, l2 may be made from the same die; or two dies'of the same contour may be used to form thesurfaces of a disk of polystyrene or the like filling the space I8 and on which the metallic bodies l0, 12 may be deposited or otherwise afiixed.

If it is desired to compensate failure of the en ergy to focus at the edge 20, the wave-guiding surfaces Hl, l6 may have contours different from those determined by the foregoing formula.

' In the operation of the scanning apparatus,

Hi to the diametrically opposite side of device 8 and exit from device 8 as a beam indicated by ray lines 38 well collimated in, and polarized with the electric vector parallel to, the plane of the scan circle. This beam rotates about the device with rotation of the rotary joint driven by motor 36 throughthe gears 34. Conversely, received or returned echo energy collimated on incidence at device 8 and polarized with the electric vector parallel to the scan circle is focused at a point on the circular edge 20 of the lspace between wave-guidingsurfaces I4, I6. If, horn antenna 26 is. at this .focal point the energy passes successively through horn antenna 26, waveguide 28, rotary joint 30 and waveguide 32 to a'receiven'if one at the moment be .connectedinstead of the transmitter. It will be apparent that, because the moving parts are light and'rotatably driven, the scanning apparatus may be made to scan at a relatively rapid rate through a 360 scanning angle. Such rapid scanning rates are diflicult to achieve with conventional structures. .5. The invention as described'includes a scanning apparatus which may scan through a 360 scan angle and a novel focusing device which has par- .ticular' advantages for this type of scanning apparatus because the focal field falls upon the circular periphery of the focusing device, and the apparatus can give high rates of scan.

What I claim is: r

1. Scanning apparatus comprising a pair of dielectrically separated metallic bodies having wave-guiding surfaces facing each otherand each rotationally symmetrical with'respect to a common axis, the peripheries of said surfaces having substantially the same radius, and a radiator or receptor closely adjacent and facing toward-the space defined between said surfaces and toward said axis respectively to direct or receive energy polarized with the electric vector thereof parallel to the planesof said peripheries to travel within the space between saidsurfaces and to exit from or be received from the side of said space radially opposite said radiator or receptor.

' 2. The apparatus claimed in claim 1, said radiator or receptor being movable to different points along a'circular path in a plane normal to and centered on said axis, said path being substantially that defined between said peripheries of said body surfaces.

3. The apparatus claimed in claim 1, said radiator or receptor being. rotatably movable along the edge of the space between said surfaces in a plane-normal to and on a path centered on said ax1s. I a

4. The apparatus claimed in claim 1,'the 'distance of separation 11 between said surfaces at'any point a distance r from said common axis being defined by the equation ll r I a .---2: v 2/e+(%)2 where R is the peripheral radius of said surfaces and e is the dielectric constant of the dielectric separating said metallic bodies. i

5. The apparatus claimed in claim 1, further comprising a solid dielectric member, said bodies comprising a metallic coating on said member.

6. The apparatus claimed in claim 1, further comprising means to drive said radiator or receptor in a circular path about said axis with a radius substantially equal to that of each said body periphery.

7. A focusing device comprising a pair of dielectrically separated metallic bodies having wave-guiding surfaces opaque to electromagnetic energy at the operating frequency and facing each other and rotationally symmetrical with respect to a common axis, said bodies having substantially the same radius, said surfaces defining therebetween a disk-like space with a circular.

edge, a dielectric being the sole filling in said space, the distance of separation between the surfaces at any point bearing a predetermined relation to the radial distance in the disk-like space from said axis to said point, so determined that rays of collimated electromagnetic energy polarized with the electric vector parallel to the plane of said disk-like space and entering said space at the edge thereof is focused substantially at the point on said edge intersected by the radius vector from said axis parallel to and in the same direction as that of said rays said predetermined relation being ripheral radius of each body.

8. An electromagnetic energy focusing device comprising two metallic bodies having rotational symmetry with respect to a central axis and symmetrical with respect to a central plane normal to said axis and having surfaces opaque to electromagnetic energy at the operating frequency and facing each other to define therebetween a space, said bodies having substantially the same radius, and a dielectric separating said bodies and being the sole filling of the said space so defined, said plane being parallel to the electric vector of the energy to be focused, the distance of separation a between said surfaces at any point a distance r from said common axis being defined by the equation e a L 2 /e+ (r/R) -2 where R is the peripheral radius of said surfaces and e is the dielectric constant of the dielectric separating said metallic bodies.

WILLIAM C. WILKINSON, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Microwave Optics Between Parallel Conducting Sheets by H. B. De Vore and Harley Iams; pages 729 to 730 in RCA Review, December 1948. 

